The knight moves to the perfect c4-square.
28... g7f8  29. g5e3 Carlsen has the kind of endgame that he likes so much. White has a technically winning position, especially in such competent hands. Black's pawn structure is full of weaknesses, and White needs to create an additional point of contact, either by advancing pawns on the kingside or by advancing c2-c3 if the queens are exchanged. 29... d6f7  30. d2f2  30... f7d8 